1. Field of the Invention
The present invention relates to light fixtures, and in particular to a multiple lamp ballast system for fluorescent light fixtures having instant start type tubes.
2. Description of Prior Art
Instant start fluorescent lamps depend on the application of a high voltage across the lamp electrodes to initiate the lamp arc and operation of the lamp. This voltage ejects electrons from the electrodes by field emission. These electrons flow through the tube, ionizing the gas and initiating an arc discharge. Thereafter, the arc current provides electrode heating. Instant start lamps, therefore, need only a single contact at each end of the tube, which reduces the wiring necessary to operate the lamps.
FIG. 1 shows a typical two lamp instant start type fixture in which two lamps 10, 12 are oriented in parallel to one another. Sockets 18, 20, 26, 28 provide mechanical support and electrical contact to the lamps 10, 12. A ballast 14 has three output leads 16, 22, 24. A first ballast lead 16 is connected to each of two sockets 18, 20 on one side of the lamps. Second and third leads 22, 24 are connected to sockets 26, 28 at the opposite ends of the lamps, respectively.
FIG. 2 shows a typical three lamp instant start type fixture in which three lamps 30, 32, 34 are also arranged (physically) parallel to one another. Sockets 36, 38, 40, 52, 54, 56 provide mechanical support and electrical contact to the lamps 30, 32, 34. A ballast 44 has four leads 42, 46, 48, 50. A first ballast lead 42 is connected to each of three sockets 36, 38, 40 on one side of the lamps. Second, third and fourth leads 46, 48, 50 are connected to sockets 52, 54, 56 at the opposite ends of the lamps, respectively.
Both configurations described above require that wiring be run from the ballast to each side of the lamps, thus requiring a wire-way and wire-way cover as a part of the fixture. Multiple lamp fixtures are high volume items in the market place, and it is desirable to reduce the cost of manufacturing these fixtures by eliminating wiring, wire-way and wire-way cover materials.
It is an object o f the present invention to provide a multiple lamp instant start type fluorescent light fixture having minimal wiring and eliminating the need for providing a wire-way and wire-way cover.
It is a further object of the invention to provide a multiple lamp ballast system for tubular instant start fluorescent lamps in which the ballast is wired to one end of the lamps only.
The present invention provides a multiple lamp ballast system having a plurality of instant start type flourescent lamps having substantially the same current characteristics, and a ballast. Each of the lamps is tubular in shape, having a first end and a second end. The ballast has at least one power input lead electrically connected to the ballast circuit, and a plurality of power output leads, also electrically connected to the ballast circuit, corresponding to the number of lamps of the fixture. Each power output lead corresponds to a different lamp. The ballast circuit is operable to supply the voltages and currents required to start and operate the instant start type lamps. The ballast circuit is designed such that the starting voltages and operating currents supplied to each output lead are approximately equal in magnitude and differing in phase by 360xc2x0/n, where n is the number of power output leads being supplied. A first plurality of electrical contacts serve to connect each output lead to a different lamp first end. A second plurality of electrical contacts serve to connect the second ends of each lamp together. Thus, a balanced n-phase system is created and it is unnecessary to run any wiring between the ballast and the second ends of the lamps.
By orienting the lamps such that the first ends are adjacent to one another, the lengths of the first plurality of electrical contacts may be minimized. By physically locating the ballast adjacent to the lamp first ends the electrical contact materials may be even further reduced.
Additional manufacturing and performance benefits may be achieved by orienting the lamps in parallel to one another such that the first ends are adjacent to one another. Electrical contact materials may also be reduced in this arrangement by physically locating the ballast adjacent to the lamp first ends than to the second ends.
Further, an improved light fixture may be achieved by utilizing the ballast system of the invention in conjunction with lamp sockets and a fixture chassis. The lamps have first and go second ends, with each end having a base pin. The lamp sockets are mounted to the chassis and have electrical contact blades therein. The lamp sockets mechanically support and electrically power, via the contact blades, the lamps. The ballast operates as previously described, with the power output leads electrically connecting the ballast circuit to the lamp first end socket blades. An electrical connector connects the lamp second end socket blades together. Once again, the resulting balanced n-phase system eliminates the need to connect the lamp second ends to the ballast.